Problem: $ A = \left[\begin{array}{rrr}1 & 1 & 2 \\ 0 & 0 & 2 \\ 0 & 2 & 1\end{array}\right]$ What is $ A^{-1}$ ?
Answer: $ = \left[\begin{array}{rrr}1 & -\frac{3}{4} & -\frac{1}{2} \\ 0 & -\frac{1}{4} & \frac{1}{2} \\ 0 & \frac{1}{2} & 0\end{array}\right]$